* Hospitalism: Spitz observed that infants who were separated from their mothers for extended periods in institutions (even if their physical needs were met) experienced severe emotional and developmental problems, a phenomenon he called "hospitalism." This research highlighted the importance of maternal bonding and emotional nurturing for healthy development.
* The "Eight-Month Anxiety": He described a stage of development around eight months of age where infants exhibit anxiety when encountering strangers, reflecting the growing awareness of separation and the development of object permanence. This provided crucial insight into the formation of attachment and the development of separation anxiety.
* The "Smiling Response": Spitz studied the development of the social smile in infants, showing how it emerges as a crucial social interaction tool and a sign of early emotional connection.
Spitz's work challenged the then-prevalent belief that infants were primarily driven by biological needs and that their emotional lives were less important. His contributions helped to establish the field of psychoanalytic child development and continue to influence our understanding of the importance of early relationships and experiences in shaping a child's mental health and well-being.